A large proportion of pregnant New Zealand women are at higher risk of poor health outcomes because they don’t know how much weight they should be putting on during pregnancy, new University of Otago research suggests.

Researchers asked 641 Dunedin and Christchurch women who were having their 12-week scans which BMI category (underweight, normal weight, overweight, and obese) they believed they fell into and what the corresponding recommended weight gain during pregnancy was.

The study found that while two-thirds of the women could correctly identify their BMI category, less than one-third (31 per cent) could identify the appropriate weight gain for that category.

The findings are published in this week’s edition of the New Zealand Medical Journal.

Study co-author Emma Jeffs says women who were overweight and obese were found to be the most likely to lack accurate knowledge of their own body size.

“This misperception may lead to an under-or-over estimation of healthy weight gain during pregnancy, which may in turn lead to increased risk of poor health outcomes,” says co-author Dr Helen Paterson, consultant obstetrician.

Dr Paterson says that as well as facing greater health risks such as high blood pressure and gestational diabetes during pregnancy, women who gain excess weight in pregnancy are more likely to have overweight and obese children.

The authors conclude “…this study indicates that more education needs to be provided and emphasis given to weighing and measuring women, and also accurately advising them of their specific gestational weight gain targets. Without this we are not fulfilling our responsibilities as healthcare professionals and essentially expecting women to ‘fly blind’”.

This study supports the importance of the New Zealand childhood obesity plan which includes a healthy weight gain in pregnancy guideline, Dr Paterson says.